The present invention relates to a disc drive microactuator system, and more particularly to an improved structure and fabrication process for integrated moving-coil magnetic microactuators.
The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a slider (which carries the head) on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. In particular, moving-coil magnetic micro-actuator designs featuring a magnet/keeper assembly and coil have been developed. Magnetic microactuators typically include a stator portion and a rotor portion, the stator being attached to the flexure and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be positioned more precisely over a track of a disc.
To accomplish this fine positioning, a magnetic circuit allows the rotor to be moved in response to a current provided to the magnetic circuit. The magnetic circuit comprises a bottom keeper, magnets, a conductive coil, and a top keeper, all vertically arranged. Present magnetic microactuators have the magnets positioned on the rotor, with the coil positioned above the rotor on a flexure. Stand-offs built on the rotor space the coil and flexure above the rotor. Currently, fabricating these types of circuits requires multi-layer processing involving a variety of alternative technologies, such as electroplating, high aspect ratio plating molds of epoxy based photo resist, as well as an extensive process flow to fabricate and integrate the magnet/keeper and coil assembly.
In addition, electrical connections from the stator to the rotor are required, either to connect to the coil or to other electrical elements, such as the read/write head. Often, these connections are in the form of traces or thin wires, which greatly increases the stiffness of the microactuator. As a result, the force the microactuator must generate to overcome the stiffness caused by such wires also increases. In addition, the wires may eventually fatigue or wear so that the read/write head begins to be held at an angle rather than held in the correct horizontal plane, which affects the flying height and stability of the slider and read/write head.
There are also several challenges in forming the coil used by the microactuators. A dense coil is desirable because the denser the coil, the higher the ability of the microactuator to move the read/write head. Current manufacturing techniques limit the density at which a coil can be created. These current manufacturing techniques typically involve depositing some sort of mold on the surface of a wafer and filling the mold with a metal, such as copper, to create the coil. However, such molding techniques are limited in their ability to achieve densely packed coils.
Thus, there is a need in the art for a microactuator having a highly dense coil which can be manufactured in bulk. In addition, it is desirable to reduce the stiffness of the beams while still allowing connections to be made as necessary.
The present invention is a magnetic microactuator for use in a disc drive. The magnetic microactuator comprises a stator and a rotor (which is movable with respect to the stator). A slider carrying the read/write head is attached to the microactuator rotor so that the slider can be finely positioned above a track on a disc by causing the rotor to move.
A magnetic circuit is used to actuate the microactuator. The magnetic circuit includes a bottom ferromagnetic keeper, a conductive coil, a plurality of magnets, and a top ferromagnetic keeper, all of which are vertically arranged in parallel horizontal planes. In response to circulation of a current through the conductive coil, the magnetic circuit causes movement of the microactuator rotor in a horizontal plane generally parallel to the surface of the disc.
The microactuator utilize embedded metal interconnects for the electrical connections and coil and incorporates a dual silicon wafer structure. The embedded interconnects and coil, as well as the structure of the microactuator, are formed using a variety of thin film technologies, such as deep-trench reactive ion etching (DT-RIE), reactive ion etching (RIE), plasma-enhanced chemical vapor deposition (PCVD), and metallo-organic chemical vapor deposition (MOCVD).
The dual silicon wafer structure includes a bottom structure and a top structure which, when joined together, form the microactuator. The bottom structure comprises the stator and rotor, as well as an embedded metal coil, bond pads, and jumper. As a result of embedding the metal coil, bond pads, and jumper into the silicon from which the bottom structure is formed, the surface of the bottom structure remains planar. Maintaining a planar surface on the bottom structure greatly simplifies the manufacturing processes involved in forming the extremely fine structural components of the bottom structure.
The top structure comprises an etched tub to provide a pocket for inserting keeper material and magnets. The top structure is also etched to form mechanical stand-offs to establish the separation distance between the magnets inserted into the top structure and the coil embedded on the rotor on the bottom the structure.
Once formed, the top and bottom structures are bonded together. Formation of the top and bottom structures can take place at the wafer level, wherein several structures are formed on a silicon wafer. If formed at wafer level, device singularization is performed after a wafer-level bonding process, using well known methods, such as break away tethers.